19713721 has 4 divisors (see below), whose sum is σ = 20085732. Its totient is φ = 19341712.

The previous prime is 19713719. The next prime is 19713731. The reversal of 19713721 is 12731791.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12731791 = 71 ⋅179321.

It can be written as a sum of positive squares in 2 ways, for example, as 14167696 + 5546025 = 3764^2 + 2355^2 .

It is a cyclic number.

It is not a de Polignac number, because 19713721 - 2¹ = 19713719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19713731) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 185926 + ... + 186031.

It is an arithmetic number, because the mean of its divisors is an integer number (5021433).

Almost surely, 2^19713721 is an apocalyptic number.

It is an amenable number.

19713721 is a deficient number, since it is larger than the sum of its proper divisors (372011).

19713721 is an equidigital number, since it uses as much as digits as its factorization.

19713721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 372010.

The product of its digits is 2646, while the sum is 31.

The square root of 19713721 is about 4440.0136261052. The cubic root of 19713721 is about 270.1403979463.

The spelling of 19713721 in words is "nineteen million, seven hundred thirteen thousand, seven hundred twenty-one".